Hold up. In your screenshot, you are translating Intercompany Supply Chain Interim_English, but your Text Unit - Translation is one level down, in Simulations and QRGs_English. Move it to inside the Intercompany... Group and see if that helps.
(I can't tell if you already have one in there, in which case you may have multiple Translation Units which could also be a problem - especially if it is trying to translate things twice...)
A couple of things to check:
I haven't seen that one before so it's not common. Perhaps try translating the Book object on its own and then do the folders and Simulations separately. If that doesn't work, take a look at this KBA to see if that helps to address the timeout issue.
If the issue is still there, raise a ticket using the Component ID KM-SEN-PRO and see if there is a way to modify the timeout value that is causing the error message to display.